Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 230958

Area Forecast Discussion
National Weather Service Seattle WA
258 AM PDT Tue Oct 23 2018

.SYNOPSIS...One last fog episode this morning before a weakening
front will arrive this afternoon and evening. This may not bring
much rain but should turn winds southerly and clear out most of
the fog. A stronger system will arrive on Thursday with wet
weather continuing into Friday. After a break on Saturday,
another front will reach the area on Sunday.


.SHORT TERM...There is widespread dense fog over the interior
lowlands once again this morning due to light winds and poor
mixing. A Dense Fog Advisory is in effect until 11 AM this
morning, mostly for the I-5 corridor. The fog will lift and
scatter this afternoon as southerly winds increase.

Meanwhile, there is a weak cold front approaching Western
Washington today. Most of the shower activity will be along the
coast today with showers spreading inland this evening. This will
likely be our first measurable rain since October 8-9. Air
quality will improve with the shower activity as a few sensors
have hit "moderate" to "unhealthy for sensitive groups".
Temperatures will be mostly in the low to mid 50s today, similar
to yesterday.

We`ll see a break in the weather on Wednesday, then a stronger and
wetter system will arrive on Thursday. This frontal system is
associated with a deep 966 mb low that is tracking NE into
northern B.C. The northern track of the low will limit winds
although it`ll likely still be breezy along the coast and north

Friday is now looking wet as another Pacific system clips through
Western WA. The forecast was adjusted as both the GFS and ECMWF
seem on board. 33

.LONG TERM...The forecast models are showing another break in the
weather on Saturday as a weak upper level ridge passes through.
Rain will likely return on Sunday as a trough forms offshore then
shifts inland. This system is cooler and will knock snow levels
down in the mountains - down to around 5,500 feet Sunday night.
The forecast will remain cool and showery through early next week
as the trough lingers over the Pac NW. Temperature trends will
remain slightly cooler than normal. 33


.AVIATION...An upper level ridge will continue to shift further east
today as a weak front approaches the coast this afternoon. Moderate
southerly flow aloft will gradually pick up and shift to the
southwest as the frontal system approaches. The air mass remains
stable and dry except for the near-surface based moisture trapped by
the inversion. Mid to high level clouds are expected to increase
over the interior this afternoon and evening, bringing deeper
moisture to the region and increasing chances for showers this

Cigs over W WA remain low as fog remains prominent in the area.
Expect IFR to LIFR conditions to linger in the region into the early
morning hours. An approaching front will then begin to induce light
southerly flow by daybreak, allowing for the fog to slowly begin
lifting with a mix of IFR, MVFR and scattering low clouds this
morning. Light rain is expected to reach the coast in the afternoon
and spread inland by early evening. Mostly VFR conditions expected
with a few pockets of MVFR as light showers are expected Tuesday
evening and overnight.

KSEA...LIFR conditions are prominent as fog currently persists near
SeaTac. Light, variable flow will turn southerly this morning and
will allow for cigs to gradually increase to MVFR conditions near
the mid to late morning hours. Mid to high level clouds are expected
to move into the area and lower in the afternoon as light rain
showers become possible this evening. SB


.MARINE...Light flow over the waters will become southerly later
tonight. A weak front will reach the coastal waters today...bringing
with it small craft advisory level winds. Models have been
persistent in this feature and as such feel good about the SCA
currently up. The front is expected to dissipate as it reaches the
coast by late afternoon and does not pose much of a threat for
increasing winds over interior waters. Another front is expected to
arrive late Wednesday and Thursday with small craft winds over the
coastal waters possibly spreading to the eastern strait...the
northern inland waters and Admiralty Inlet Thursday. Lighter flow is
expected Friday.  SMR


WA...Dense Fog Advisory until 11 AM PDT this morning for Bellevue and
     Vicinity-Bremerton and Vicinity-Everett and Vicinity-
     Seattle and Vicinity-Southwest Interior-Tacoma Area.

PZ...Small Craft Advisory until 5 PM PDT this afternoon for Coastal
     Waters From Cape Flattery To James Island 10 To 60 Nm-
     Coastal Waters From Cape Flattery To James Island Out 10 Nm-
     Coastal Waters From James Island To Point Grenville 10 To
     60 Nm-Coastal Waters From James Island To Point Grenville
     Out 10 Nm-Coastal Waters From Point Grenville To Cape
     Shoalwater 10 To 60 Nm-Coastal Waters From Point Grenville
     To Cape Shoalwater Out 10 Nm.


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